Bi-Wire with two pairs of speaker cables

Bollocks! When will audiophiles realize that changes they make to their system is specific to their system only?!?!?!

The reason for BiWiring is to stop woofer current from modulating tweeter current.

It is totally permissible to use two different cables.

Each and every combination will have various effects.
Jumping one of the legs at the speaker will sound different on every speaker.
Separating the cables will change the inductance and thus the sound. I like mine interwoven.
There is no need to have dual amp outputs, two spades on one terminal or two leads into one spaded is fine. Adding a second terminal adds additional LCR which may or may not alter the sound depending on the components chosen.

In ALL cases, audibility is program, system and listener dependent.

Ignore fan-boy recommendations, experiment and keep what sounds best to you.

Please see http://ielogical.com/Audio/CableSnakeOil.php/#BiWire for a BiWire analysis.

Not a problem.

Is there any technical reason why wire jumpers are better than good quality metal straps ?

If the plating or base metal was poor, there could very significant sonic effects.

Well done crimps or soldered connections are functionally one. In a crimp the metal is mashed into one with the spade.

A pair of metal strips has a quite different LCR than wire. Strips have no dielectric, so the wave travels in air rather than the dielectric. Strips are flat, so therefore have an asymmetric flux field. etc.

Don't believe any manufacturers claim as they have not test their product in your system. In addition, the evaluator does not have your ears or preferences.

Bottom line is if one sounds better, use it. If not don't.

Do you think that the designer/manufacturer of high-quality loudspeakers would knowingly use something that degrades the sound?

Stuff happens.

We once got a new batch of NE5532 chips that had 10x the current draw. My company replaced 7 million Philips capacitors that did not meet the life spec. Of those replacements, several tens of thousand had to be replaced because if the bung was over the negative rail trace, it sucked out the electrolyte, shorted the buss and occasionally started a fire.